Atomic Structure Flashcards
Atomic model over the years
1803 - John Dalton and the billiard ball
1904 - JJ Thompson and the Plum Pudding model
1911- Earnest Rutherford and the nuclear model
1913 - Neil Bohr and the Bohr model
Relative mass and charge of Protons, neutrons, and electrons. Why is the term relative used?
Protons 1, +1
Neutrons 1, 0
Electrons 1/1840, -1
The numbers are too small therefore a relative is used.
What are isotopes?
An element with the same number of protons but different numbers of neutrons.
How do isotopes react chemically and physically?
Chemically they react the same because of the number of electrons in their valence.
Physically they are different as the neutrons can affect relative mass, so melting points and densities can be affected.
What are cations and anions
+ -
What is the mass spectrometer
It’s a machine that measures
1. Mass of an atoms and molecules
2. Ar and Mr
3. Identifies elements
4. Very accurate
What is the definition of relative atomic mass (Ar)?
Average mass of 1 atom ÷ 1/12th mass of carbon-12
What is the definition for Mr
Average mass of 1 molecule ÷ 1/12th mass of carbon-12
How many stages does the mas spectrometer have and what are they?
4 stages
1. Ionisation
2. Acceleration
3. Ion drift
4. Detection
How many types of Ionisation are there?
There are two types: Electron impact and Electron spray
Describe the process of Electron impact?
- Sample is vaporised and hit with electron gun
- Electrons from gun knock off electrons from sample molecules
- Molecules (sample) is now positively charged
(usually electrons and protons are equal but knocking off one negative electron makes it positive as there are now more protons.)
Describe the process of Electron spray?
- Sample is dissolved in a solvent and high voltage is applied
- High voltage rips off proton from solvent and attaches to the sample molecule
- Sample is now positively charged
Electron impact Vs Electron Spray
EI:
1. causes fragmentation
2. Used for low Mr compounds
3. gaseous state (loss of electrons)
ES:
1. Gentle and prevents fragmentation
2. Used for polymers and biological molecules (DNA)
3. Gaseous state (Gains proton)
What happens in stage two of the mass spectrometer?
All molecules are accelerated to have the same kinetic energy.
What happens in stage three of the mass spectrometer?
- Ste off at the same time
- Lighter ions move faster and start to separate
- Lighter ions reach the detector first
(Lighter ions move faster=shorter time of flight)